"Until now, we haven't known exactly what effect these energy drinks have on the function of the heart," said Jonas Dorner, of the cardiovascular imaging section at the

University of Bonn, Germany, which is led by the study's principal investigator, Daniel K Thomas.

"There are concerns about the products' potential adverse side effects on heart function, especially in adolescents and young adults, but there is little or no regulation of energy drink sales," Thomas said.

"The amount of caffeine is up to three times higher than in other caffeinated beverages like coffee or cola.

"There are many side effects known to be associated with a high intake of caffeine, including rapid heart rate, palpitations, rise in blood pressure and, in the most severe

cases, seizures or sudden death," Dorner said.

For the study, which is ongoing, Dorner and colleagues used cardiac magnetic resonance imaging (MRI) to measure the effect of energy drink consumption on heart function in 18 healthy volunteers, including 15 men and three women with a

mean age of 27.5 years.

Each of the volunteers underwent cardiac MRI before and one hour after consuming an energy drink containing taurine (400 mg/100 ml) and caffeine (32 mg/100 ml).

Compared to the baseline images, results of cardiac MRI performed one hour after the study participants consumed the energy drink revealed significantly increased peak strain and peak systolic strain rates (measurements for contractility) in the left ventricle of the heart.

The heart's left ventricle receives oxygenated blood from the lungs and pumps it to the aorta, which distributes it throughout the rest of the body.

"We don't know exactly how or if this greater contractility of the heart impacts daily activities or athletic performance," Dorner said.

"We need additional studies to understand this mechanism and to determine how long the effect of the energy drink lasts," Dorner said.

The researchers found no significant differences in heart rate, blood pressure or the amount of blood ejected from the left ventricle of the heart between the volunteers' baseline and second MRI exams.